Cellulosic and lignocellulosic feedstocks and wastes, such as agricultural residues, wood, forestry wastes, sludge from paper manufacture, and municipal and industrial solid wastes, provide a potentially large renewable feedstock for the production of valuable products including alcohols to be used as fuels, and other chemicals. Cellulosic and lignocellulosic feedstocks and wastes, composed of carbohydrate polymers comprising cellulose, hemicellulose, and lignin are generally treated by a variety of chemical, mechanical and enzymatic means to release primarily hexose and pentose sugars in a hydrolysate which can be fermented to produce useful products using a biocatalyst.
In addition to the metabolizable sugars that are present in hydrolyzed biomass, the hydrolysate includes undigested lignin and other biomass components that carry through to product isolation and downstream processes. These hydrolysate components, mixed with the biocatalyst and other fermentation broth components, need to be processed in addition to the main product. Particularly in the production of fuel alcohols, where production volumes are very high, net water use is important as is the use of fossil energy to produce the fuel alcohol. To minimize net water use, fermentation broth with product removed may be recycled to earlier stages in the process, or solids may be separated from this broth and the liquid stream recycled to earlier stages in the process (referred to as back-set). Also, the liquid stream may be purified by various methods prior to recycle. The solid stream, containing a large percentage of lignin, has low nutritional value as an animal feed, but may be used as a fuel which is burned to provide energy in the overall production process.
Handling processes exist for standard fermentation broth, which does not include biomass hydrolysate, and for biomaterial waste streams. The mix of components in these systems differs from those in a biomass hydrolysate fermentation broth, thereby requiring development of processes specifically suitable for efficient handling of the hydrolysate broth mixture.
For separation of liquid and solid fractions in the dry milling process for ethanol production, typically centrifugation is used. The high speed horizontal decanter type centrifuges typically used are not efficient in removing suspended solids and are not efficient in dewatering the solids. WO2008076716 discloses use of anionic polymer flocculants to improve agglomeration of solids in centrate from the centrifuges, to aid in subsequent solid/liquid separation.
Heat may be used in processing in known systems, usually in the presence of a flocculating agent as in GB1413236 where heating the culture broth (non-hydrolysate), which includes a surface active agent, at a temperature of from 70° C. to 95° C. for 10 to 30 minutes is optionally used in recovering microbially produced L-lysine. U.S. Pat. No. 4,374,981 discloses methods of separating inosine and guanosine from fermentation broth (non-hydrolysate) which includes heating fermentation broth at between 90° C. and 110° C. for five to ten minutes, and separating by ultrafiltration.
US2007017825 discloses processes for treating biomaterial waste streams such as swine waste, cheese whey, and barn animal biomaterial waste. The processes include degrading at least a portion of the biomaterial waste stream into other components or materials that may be reintroduced into a fermentation process. Treatment may include pH adjustment and heat treatment followed by precipitate/aggregate removal based on density such as by centrifugation.
There remains a need for efficient, low-cost processes for treatment of production side streams from fermentation broth that includes lignocellulosic biomass hydrolysate, particularly where large volumes of broth must be processed.